How to find the difference between two times:
Subtract the minutes of the earlier time from the minutes of the later time.
(If the earlier time has more minutes than the later time,
you can "borrow" from the hour by subtracting 1 from the hour of the later time
and adding 60 to the minutes of the later time.)
After you have found the difference in the minutes, subtract the
hour of the first time from the hour of the second time.